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Full text of "Text Book Of Mechanical Engineering"

526                        Moore's Pulley Block.

If A and L are nearly equal, we have a high velocity ratio.
In the block, the eccentric G, corresponding to crank ef, is rotated
by hand chain round H, so that A and L are turned oppositely,
each by half their relative motion, and w's rise is due to this.

P's distance = 2 ?r R

,TTi    ,.               2 TT r x L's revs.

W s distance =------------------


i xr i  ^   -        p's  dist-           2R

and Vel. Ratio =

W's dist.     r x L's revs.
In the example BC has 14, A 15, and L 16 teeth.    If R = r
Vel. Ratio =        ? = 32 : i

1        14 X 16

Another reverted train is obtained by bevel wheels, as in
Fig. 526, being applied as driving gear to traction engines and
tricycles. B is the arm, and A, L the first and last wheels respec-
tively. When the front road wheel is steered ahead, A, B, and L
are practically locked, and the two hind road wheels move with
equal velocities; but if the front wheel be steered, say, to the left,
A becomes fixed and L revolves at double speed, thus steering
the engine in a much smaller curve. Fig. 527 shews a detailed
section through the hind axle.

Fig. 528 is a disguised form of sun and planet motion, where
L is annular and the slider-crank chain is employed. Considering
A fixed, as in Fig. 520,

T>                              A

L s revs. = i - -=-

If A an<J L are nearly equal, a slow movement of L is obtained,
as in Fowler's second coiling gear, Fig. 529. Eccentric B serves
as crank, and D as connecting rod; A and L have the same
meaning as in Fig. 528, and the cam and lever are as previously
described. (See p. 1108.)

(6.) Belt Gearing has the disadvantage of slip, but is
practically .noiseless, and will transmit power a considerable
distance (say 30 ft.) without intermediate support.